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Driver117
Samba Member
Joined: December 13, 2024
Posts: 3
Location: UK
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 Posted: Fri Dec 13, 2024 3:38 pm Post subject: 1300 single port race engine |
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Hi,
I've been reading The Samba forums for a while but this is my first post.
I race a Formula Vee and I'm looking at a new exhaust. All Formula Vee's around the world run a 4 into 1 exhaust, regardless of engine size or silencer requirements.
I'm wondering, how does a Baja exhaust effect performance?
I can't find anything anywhere that says how a split exhaust like a Baja/off-road exhaust effects performance of a beetle engine so any help will be appreciated
Thanks |
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krusher
Samba Member
Joined: September 24, 2002
Posts: 7662
Location: europe
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| Posted: Tue Dec 17, 2024 7:30 am Post subject: Re: 1300 single port race engine |
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They reduce performance, splitting the exhaust pulses into 2 banks goes against all the basics of exhaust scavenging.
4-1 headers are also using preferred over 4-2-1 headers for racing.
Baja would be two 2-1 banks.
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halfassleatherworks
Samba Member
Joined: December 09, 2018
Posts: 702
Location: Reno NV
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Driver117
Samba Member
Joined: December 13, 2024
Posts: 3
Location: UK
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| Posted: Mon Dec 23, 2024 3:28 am Post subject: Re: 1300 single port race engine |
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Thanks both for your replies.
The comments from Vanapplebomb describe exactly what I was thinking:
The 4>1 is common in racing, but the length of the primaries needs to be very long, longer than ideal, and secondaries are much shorter than ideal. This setup does narrow the powerband.
I was curious to know if merging just 1 & 2 with ideal length primary and secondaries would be better than "not ideal" length 4>1 |
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RolandD
Samba Member
Joined: January 15, 2017
Posts: 272
Location: Menomonee Falls, Wis
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| Posted: Mon Dec 23, 2024 3:40 pm Post subject: Re: 1300 single port race engine |
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Ok, what RPM do you want to maximize?
Roland |
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Driver117
Samba Member
Joined: December 13, 2024
Posts: 3
Location: UK
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| Posted: Thu Jan 02, 2025 1:53 am Post subject: Re: 1300 single port race engine |
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| RolandD wrote: |
Ok, what RPM do you want to maximize?
Roland |
That's the thing, at the moment I'm not really sure! It was more a generic question about how it would effect the engine to see if I could exploit that in any way.
To give the full detail, my family build my engines, we don't use the bespoke race engine tuners because we like the challenge, and the cost! In a Formula Vee we've tried the split carb/short intake and single carb/long intake, various cams + timing, injection etc and have slowly improved the car's laptimes. However, this has been alongside suspension changes too to make the car more drivable all round. I've uploaded a couple of videos on youtube: https://youtu.be/c2rfLnq0fBI
We have peak torque at 5000rpm and peak power at 6000rpm as torque really drops off over 6k.
The exhaust is something we've never changed, still a homemade thing that came with the car - regular steel pipe, shop bought bends clearly mig welded together so it's an area that clearly needs improving.
We could fairly easily upgrade with a like for like and see marginal gains 1 or 2% maybe. But if we could do something to widen the power band in either direction, we can make other changes to coincide with it.
I'm just thinking outside the box, and trying to do something a bit different. |
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Willin
Samba Member
Joined: October 10, 2019
Posts: 180
Location: Bozeman Mt
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| Posted: Thu Jan 02, 2025 5:59 pm Post subject: Re: 1300 single port race engine |
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Hi
Just passing through your thread.
You should ask Alstrup over in Performance.
He knows this stuff.
And, Welcome!
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Alstrup
Samba Member
Joined: July 12, 2007
Posts: 7586
Location: Videbaek Denmark
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| Posted: Fri Jan 03, 2025 6:04 pm Post subject: Re: 1300 single port race engine |
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Pairing the cylinders 1-2 & 3-4 into a 4-2-1 will only barely equal a 4 into 1 header on hp. Usually you loose midrange torque, but in a few cases with very little cam overlap the torque does not suffer.
whether you want to, or can take advantage of a 4-2-1 header you would want to ask youself: Is my rpm band in the window of the 2upper side" of where a 4 - 1 header works, or does the pick up between gears drop intothe low torque (or resonance)area.? If it does you can likely improve the mid range power with a 4-2-1 done the right way.
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